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APPENDIX

side-chains where only one side-chain is to be converted into
carboxyl on account of their less energetic action.

The oxidation of a halogen-substituted side-chain by the usual
oxidising agents is much more readily accomplished than that
of a simple alkyl group. A similar case is that of naphthalene
telrachloride, C10HiSCl4, which, though an additive compound, is
much more readily converted into phthalic acid than naphthalene
itself.

PREPARATION 91.

m-Nitro-, m-Amino-, m-Hydroxy-beiizoic Acids.—

This series of compounds merely furnishes an exercise in the
processes previously described and illustrates the application of
the same reactions in the case of a substituted benzene derivative
containing a nitro-groiip. It also illustrates the manner in which
meta-compounds of benzoic acid may be indirectly prepared
where a direct method is inapplicable.

PREPARATION 93.
Benzoin.—As a small quantity of potassium cyanide is
capable of converting a large quantity of benzaldehydeTinto
benzoin, the action of the cyanide has been explained as follows :
The potassium cyanide first reacts with the aldehyde and
forms a cyanhydrin, which then condenses with another molecule
of aldehyde, hydrogen cyanide being finally eliminated
(Lap worth),
/OH                                         /OH
CUIISCH<        + QH8CHO == QH5.Cf------CH(OH)C6Ha.
\CN                           XCN
= QH5.CO.CH(OH).QH5 + HCN.
The same reaction occurs with other aromatic aldehydes
(anisaldehyde, cuminol, furfurol, &c.)«
Benzoin yields hydrobelizbin on reduction with sodium
amalgam, and desoxybenzoin, C(!Hr>CO.CH.,.C(iH5, when reduced
with zinc and hydrochloric acid.
The latter, which contains the group CO.CH.,.C(iH-, behaves
like malonic ester, the hydrogen of the methylene group being-
replaceable by sodium, and hence by alkyl groups.